Magnetic mirror plasma source and method using same

ABSTRACT

A magnetic mirror plasma source includes a gap separating a substrate from a cathode. A mirror magnetic field extends between the substrate and the cathode through the gap. The magnetic field lines at a proximal surface of the substrate are at least two times as strong as those field lines entering the cathode. An anode is disposed such that a closed loop electron Hall current containment region is formed within the magnetic field.

FIELD OF THE INVENTION

Applicant's invention relates to a magnetic mirror plasma source.

BACKGROUND OF THE INVENTION

The related prior art is grouped into the following sections: magneticconfinement and the Penning cell source, facing target sputtering,plasma treatment with a web on a drum, and other prior art methods andapparatuses.

Magnetic Confinement and the Penning Cell Source

Confinement of electrons and ions using magnetic mirrors is presented insection 3.4.2 of J. Reece Roth, Industrial Plasma Engineering, Volume 1:Principles, IOP Publishing, Ltd. 1995.

Facing Target Sputtering

U.S. Pat. No. 4,963,524 to Yaniazaki teaches a method of producingsuperconducting material. An opposed target arrangement is used with thesubstrate positioned between the electrodes in the magnetic field. Themagnetic field is symmetrical between the electrodes, and the substrateis in the middle of the gap. With the substrate in this position, theHall current generated within the magnetic field tends to be distortedand broken. When this happens, the plasma is extinguished and/or thevoltage is much higher.

Plasma Treatment With A Web On A Drum

In U.S. Pat. Nos. 5,224,441 and 5,364,665 to Felts et al., a flexiblesubstrate is disposed around an electrified drum with magnetic fieldmeans opposite the drum behind grounded shielding. In this arrangement,the shield opposite the drum is either grounded or floating. Thesubstrate is supported by the surface without a mirror magnetic fieldemanating from the substrate.

In U.S. Pat. No. 4,863,756 to Hartig et al., the substrate iscontinuously moved over a sputter magnetron surface with the surfacefacing the magnetron located inside the dark space region of thecathode. In this way, the magnetic field of the magnetron passes throughthe substrate and is closed over the substrate surface constricting theplasma onto the surface.

Other Prior Art Methods and Apparatuses

U.S. Pat. No. 5,627,435 to Jansen et al. discloses a hollow cathodesource operating at high, diode plasma regime pressures (0.1-5 Torr).The plasma is created inside the hollow cathode holes and then isconducted to the substrate with the help of magnets under the substrate.Multiple individual magnets separated from each other are depicted.

U.S. Pat. No. 6,066,826 to Yializis discloses a plasma treatment sourcefor web materials. The source magnet configuration is further defined inthe referenced SVC Technical Conference paper (1998) by Decker andYializis. A magnetron magnet array is positioned under a flexible websimilar to Hartig et al. in U.S. Pat. No. 4,863,756. A hollow cathodeelectrode is positioned above the web.

U.S. Pat. No. 6,077,403 to Kobayashi et al. shows a magnetron incombination with a second magnetic field. In this patent, the secondfield passes through the substrate to a supplemental electrode. Thisapparatus is not a stand-alone plasma source—it assists with ionizingand directing sputtered material to the substrate. Also, the firstembodiment has the mirror field with a stronger magnetic field at thesupplemental electrode than at the surface of the substrate.

In U.S. Pat. No. 4,631,106 to Nakazato et al., magnets are located undera wafer to create a magnetron type field parallel to the wafer. Themagnets are moved to even out the process. The opposed plate isgrounded, and the wafer platen is electrified.

U.S. Pat. No. 4,761,219 to Sasaki et al. shows a magnetic field passingthrough a gap with the wafer on one electrode surface. In this case, theelectrodes are opposed to each other. The wafer is placed on the lesscompressed magnetic mirror surface, and the opposed surface across fromthe wafer is grounded.

U.S. Pat. No. 4,853,102 to Tateishi et al. uses a cusp field to assistsputter deposition into high aspect ratio holes. The flux lines leavingthe substrate do not enter a negatively biased electrode.

U.S. Pat. No. 5,099,790 to Kawakami shows a microwave source with amoving magnet below the wafer to even out the coating on the wafer. Inanother figure, the substrates are moved over a stationary magnet(s). Inthis source, the plasma is generated in a separate plasma generationchamber and then directed to the wafer substrate with the assistance ofthe magnet under the substrate.

In U.S. Pat. No. 5,225,024 to Hanley et al., ExB containment is achievedby forcing the B flux into a parallel path over the substrate surface.U.S. Pat. No. 5,437,725 to Schuster et al. discloses a metal web drawnover a drum containing magnets. The web is electrified, and the opposedshield is at ground potential.

The source disclosed in U.S. Pat. No. 5,900,284 to Hu produces severalmagnetron type confinement traps on the surface above the magnets.

SUMMARY OF THE INVENTION

Applicant's apparatus includes a plasma source apparatus comprisingfirst and second surfaces with a gap between the surfaces, wherein thefirst surface comprises a substrate and wherein at least the secondsurface is connected to a power supply so as to contain electrons; athird surface connected to the power supply, a magnetic field passingthrough both the first and second surfaces and through the gap betweenthe surfaces, wherein at least a portion of the magnetic field passingthrough the substrate is at least two times stronger at the substratesurface than at the second surface along that field line and is strongenough to magnetize electrons; and an electric field created by thepower supply connected between the second surface and the third surface,wherein the electric field penetrates into an electron confining regionof the magnetic field so that a created Hall electron current iscontained within an endless loop.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from a reading of the followingdetailed description taken in conjunction with the drawings in whichlike reference designators are used to designate like elements, and inwhich:

FIG. 1A shows a section view of a simple source of a preferredembodiment;

FIG. 1B shows a simplified view of electron movement within the mirrorfield;

FIG. 1C is an enlargement of a portion of FIG. 1B;

FIG. 1D shows a top view of the simple mirror source of FIG. 1A.

FIG. 2A shows a section view of a wafer ionized physical vapordeposition apparatus of a preferred embodiment

FIG. 2B shows a top view of the apparatus of FIG. 2A with the topcathode plate made transparent for clarity.

FIG. 2C shows an isometric view of the wafer sputtering apparatus ofFIG. 2A.

FIG. 3A shows a section view of a planar substrate sputter depositionapparatus.

FIG. 3B shows an isometric view of the apparatus of FIG. 3A.

FIG. 4 shows a section view of a dual source of a preferred embodiment.

FIG. 5 shows a section view of an apparatus for sputter deposition on aflexible web substrate.

FIG. 6 shows a section view of another preferred embodiment

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

This invention is described in preferred embodiments in the followingdescription with reference to the Figures, in which like numbersrepresent the same or similar elements.

International Application Number PCT/US02/11473, in the name of Madocksand assigned to the common assignee hereof, is hereby incorporated byreference. International Application Number PCT/US02/11541, in the nameof Madocks and assigned to the common assignee hereof, is herebyincorporated by reference. International Application NumberPCT/US02/11542, in the name of Madocks and assigned to the commonassignee hereof, is hereby incorporated by reference.

In the prior art many magnetically confined plasmas are confined in twodimensions by the magnetic field and electrostatically in the thirddimension. A planar magnetron, for instance, confines the electrons inthe racetrack with arcing magnetic field lines and the electrostaticpotential of the cathode target

While the traditional magnetic confinement method is ideal for manyapplications, some are not best served with this arrangement. Theembodiments of Applicant's invention described herein present a newapparatus and method to confine electrons to produce a low pressure,dense, relatively low voltage plasma. With these preferred embodiments,a combination of electrostatic and mirror magnetic confinement isimplemented. The result is a novel plasma source that has unique andimportant advantages enabling advancements in sputtering, PECVD,etching, and plasma treatment processes.

FIG. 1A shows a simple implementation of one preferred embodiment.Source 10 is located in a process chamber at a reduced pressure. Anon-magnetic substrate 1 is placed over a magnet 5. A high permeabilitymaterial such as steel serves as the cathode 3 and is positioned oversubstrate 1 at sufficient distance to allow a plasma to form between thecathode 3 and substrate 1. Anode 11 is a ring of wire positioned aroundthe periphery of cathode 3. In this configuration, magnetic field lines12 are formed between the magnet 5 and cathode 3. The field strength ofthese lines is stronger at the surface of the substrate 1 than at thecathode 3 forming a mirror magnetic field with the compressed end on thesubstrate 1. When a plasma voltage is impressed between cathode 3 andanode 11, a plasma 14 lights between the cathode 3 and substrate 1. Inthis embodiment, rather than the substrate 1 plasma facing surface 208being held at cathode potential to reflect electrons, this surface 208can be left electrically floating. An opposing surface 210 exists insubstrate 1 and is shown parallel to surface 208. The electroncontainment is achieved by using the magnetic mirror effect The resultis that electrons are contained in all degrees of freedom by eithermagnetic and electrostatic Lorentz forces or by the magnetic mirrorformed over the substrate.

Referring now to FIGS. 1B and 1C, an electron 24 emitted from cathodesurface 21 is confined to travel along magnetic field line 25. As theelectron 24 moves along field line 25 from a region of weaker magneticfield Bo toward a stronger magnetic field Bm, the electron's axialvelocity Va is converted to radial gyration velocity Vr around the fieldline 25 and a longitudinal thermal velocity component Vt. If the axialvelocity Va component Vt reaches 0 before the electron 24 hasencountered substrate 22, the electron 24 is reflected back toward theweaker field region. As the ratio of strong to weak magnetic fieldincreases, more electrons are reflected. This magnetic mirror effect isgreatly assisted in the preferred embodiments by the electric fieldsurrounding the magnetic field. This is depicted in FIG. 1A by arrows 17and dashed line 15. This electric field imposes a radial force onelectrons that encourages the radial velocity and results in betterelectron containment by the mirror effect. This can be seen in FIG. 1Bas a cone of bright plasma 27 surrounding the inner plasma region 26.

This embodiment uses these characteristics to confine a low pressureplasma for the processing of a substrate. In source 10, a rare earthmagnet 5 is used to create a strong magnetic field region at the plasmafacing surface 208 of substrate 1. Further from the magnet, the fieldprogressively weakens and spreads out to cathode plate 3. When a voltageranging from ˜400V-2000V or higher is impressed between the cathode 3and anode 11 and the chamber pressure is approximately between 3 and 100mTorr, electrical breakdown occurs, and a plasma is maintained in region14. As electrons are created either by secondary emission from thecathode 3 or by collisions in the plasma, they are confined withinplasma region 14 and generate an endless Hall current within plasma 14.

FIG. 1D shows a top view of source 10 with cathode plate 3 drawntransparent and substrate 1 removed for clarity. The magnetic field 12in this view appears as crosses and dashed lines from magnet 5 tocathode 3. The dense cluster of crosses at magnet 5 indicates a strongermagnetic field. At the cathode 3 the magnetic field 12 is less dense.Anode 11 circumvents cathode 3. Power supply 16 is connected betweencathode 3 and anode 11. With the power supply 16 on and process gas at asuitable pressure, plasma 14 lights in the gap between substrate 1 (notshown in this view) and cathode 3. This top view illustrates the closeddrift nature of Applicant's source technology. As is well known inmagnetron sputtering, the low impedance and uniform nature of thesputter magnetron are due to the endless Hall electron current loopcreated by the racetrack magnetic field over the cathode target

The present invention also produces a closed drift electron containmentRather than by a racetrack shaped magnet array however, the closed loopelectron container is created within a dipole magnetic field. Anelectron 24, after accelerating away from cathode 3 surface, attempts tofollow electric field 17 to anode 11. Initially, near the cathodesurface, the electric field 17 is parallel to the magnetic field 12 andthe electron 24 is able to move away from the cathode 3. Further fromcathode 3, the magnetic field 12 begins to compress toward magnet 5while the electric field 17 diverges toward anode 11. As the electricfield 17 diverges, the electron is prevented from following the electricfield by the crossing magnetic field 12 and Lorentz forces induce acycloidal motion to the electron. As is seen in FIG. 1D, the simpledipole magnetic field creates an endless containment loop as thecycloidal electron 24 motion returns upon itself. This fundamentaladvancement is important to the operation of the mirror source. Themagnetic arrays of all the figures in this application produce thisclosed drift electron containment region.

Referring again to FIG. 1A, when the substrate is floated or connectedto the electrode opposed to electrode 3, at least a portion of themagnetic mirror created between the plasma facing surface of substrate 1and the plasma facing surface of cathode 3 must exceed a ratio of 2:1.This ratio is defined as the magnetic field strength at a point on theplasma facing surface of substrate 1 denoted at 202 at surface 208versus the strength of that same field line as it enters the cathode 3surface denoted at 204. A weaker ratio than 2:1 results in too fewelectrons being reflected by the magnetic mirror, and a low pressureplasma cannot be sustained.

This embodiment confines sufficient electrons such that a low pressureplasma is sustained In trials of many configurations, the ratio of atleast 2:1 between the strong field over the substrate and the weakerfield in the gap is important. As the ratio increases, the confinementimproves. With rare earth magnets and substrates of thicknesses lessthan ½ inch, it is relatively easy to achieve ratios up to or exceeding10:1. If the substrate is connected either in parallel to electrode 3 orto a separate power supply so that the substrate is biased toelectrostatically confine electrons, the mirror field can be less thanthe 2:1 ratio.

The confinement obtained using this preferred embodiment is not asefficient as traditional electrostatic confinement. While with magneticmirror ratios exceeding 2:1 and the anode placement accentuating theradial electron velocities produces confinement sufficient for a lowpressure plasma, a substantial electron flow out of the plasma into thesubstrate is apparent.

For example, the pressure required to sustain the plasma is higher thana typical magnetron source. Where a magnetron source operates at 1-5mTorr, the magnetic mirror source operates at pressures above 3 mTorrwith typical pressures of 10 mTorr. In addition, the voltage of themirror source is higher. A modified Penning discharge as shown in U.S.patent application Ser. No. 10/036,067, which is hereby incorporated byreference, can sustain a plasma at less than 400V. The mirror source lowvoltage operation is closer to 500V-1500V.

While the effect of reduced plasma confinement efficiency can bedisadvantageous for some processes, it is beneficial to Applicant'sinvention. Looking at the configuration of FIG. 1A, sufficient electroncontainment is achieved to create a dense, Hall current contained plasmawhile the “poor” confinement results in a high electron flow out of theplasma directed at the substrate 1. This is an ideal arrangement formany plasma processes. In the dense plasma formed directly over thesubstrate etching compounds, PECVD reactants, or plasma treatment gasesare efficiently activated. Simultaneously, the high electron and ionflow sweeps the activated particles onto the substrate. An analogy isthe plasma, constrained by the cathode electrode and the mirror magneticfield, is like a pressurized bottle. At the substrate, the compressedmirror field forms the nozzle on the bottle, both restraining the flowand directing the flow out of the bottle.

Another aspect of this embodiment is that while the particle current tothe substrate is high, the particle energy to the substrate is lowerthan sources energizing the plasma through the substrate. In thisembodiment, the substrate is electrically floating. The floatingpotential of ˜10V is low enough to largely rule out substrate or coatingablation or substrate damage due to impinging high energy particles.This is critically important to processes involving semiconductor wafersand low temperature substrate materials.

Note that the substrate can also be biased negatively with the samepower supply 16 (DC in the case of a conductive substrate) or adifferent power supply. If the substrate is negatively biased, moreelectrons are repelled from the substrate and contained within theplasma. This can be useful to produce increased ion energies impingingthe substrate. For non-conductive substrates, an AC, RF or pulsed DCpower supply can be used. The advantage of floating the substrate isthat thick, large, non-conductive substrates such as architectural glassor flexible polymer web can be used without the cost or complexity of abackside AC power supply. In particular, when an insulating substrate istoo thick to pass even an RF signal, the preferred embodiment can beapplied.

The substrate can also be grounded or connected as the anode in the FIG.1A circuit The fundamental containment of the magnetic mirror continuesto operate with the substrate as the anode. In this mode, the electroncurrent to the substrate increases. While a sustained glow ismaintained, the voltage is higher, a strong magnetic mirror is required,and/or the chamber pressure must be higher than when the substrate isfloating or negatively biased. For some substrates, metal sheet forinstance, a grounded substrate is much easier to configure. For others,plastic web or glass, the floating option is easier.

In any of these electrical configurations, the electron and ion flowonto the substrate is concentrated into the physical dimensions of themagnet pole as it emanates from the substrate. As the magnet pole isextended for wide substrates, the dense plasma region on the substratetakes the shape of a long bar. To obtain uniformity in the crossdirection to the bar, the substrate must move in relation to the plasma.This is shown in later figures. The field lines 12 shown define theelectron-confining region of the magnetic field.

Only the field lines that pass from the substrate to cathode 3 areshown. There are other field lines that do not pass through cathode 3,but these are not important. Electrons caught in these lines simply arecollected at the substrate or swept to the power supply and are notcontained long enough to help sustain a plasma.

The operating pressure for the preferred embodiments is belowapproximately 100 mTorr. Above this pressure the free mean electron pathbecomes considerably shorter than the magnetized electron Larmor radiusand the effects of magnetic confinement are less visible. This comportswith the classical definition of a magnetically confined plasma: Aplasma is magnetically confined when the free mean electron path isgreater than the Larmor electron gyro radius. References herein to amagnetic field strong enough to magnetize electrons means a magneticfield wherein the free mean electron path is greater than the Larmorelectron gyro radius.

FIGS. 1A, 1B, 1C, and 1D, show a simple arrangement to explain thepreferred embodiment Later figures depict several sources implementingthe preferred embodiment to process wafers, flat substrates, andflexible substrates. While an attempt has been made to show the breadthof applications that can be addressed with the preferred embodiment,many more will be apparent to one skilled in the art. The preferredembodiment presents an entirely new genus of magnetically confinedplasma source that will have as many species as the traditionalmagnetron/Penning confinement method.

FIG. 2A shows an embodiment configured for ionized physical vapordeposition (“IPVD”) onto round planar substrates such as silicon wafers.Wafer 76 is placed on non-magnetic stage 75. A magnetic field 78 ispassed through the wafer, through the gap between the wafer and sputtertarget 83 to cover 72. Target 83 is bonded to cover 72 to improvethermal conductivity between target 83 and cover 72. Cover 72 is made ofa high permeability material such as 400 series stainless steel and iswater cooled. Wafer stage 75 is also water cooled. Water cooling ofsputter sources is well known in the art and details are not shown. Themagnetic field 78 in the gap between the substrate 76 and target 83 isgenerated by magnet array 80 and is assisted by high permeabilitymembers cover 72, steel shunt circle 81, shunt 74. Shunt 74 and magnetarray 80 rotate under the stationary platen 75 to obtain a uniformcoating on substrate 76. Power supply 70 is connected between cover 72and shunt 81 to create an electric field 79. This can be a DC, pulsedDC, AC or RF power supply.

As explained in FIG. 1A, by producing a strong magnetic mirror fieldover the wafer substrate 76, a plasma 77 is confined within the magneticfield in the gap between target 83 and substrate 76. This plasma is ofrelatively low impedance compared to diode plasmas and the plasmadensity is high due to the endless, closed drift confinement ofelectrons within the dipole mirror field region. As previouslydiscussed, due to the magnetic mirror electron confinement at the wafer76 surface, stage 75 and wafer 76 can be electrically floated orseparately biased with bias power supply 82. Switch 83 is included inthe electrical circuit to illustrate these options. In the case of IPVD,a 50-460 kHz AC power supply is often used for bias supply 82. Currentat this frequency readily passes through a silicon wafer and, with theappropriate blocking capacitor, allows a controllable, negative DC biasto be applied to the wafer 76 surface. This bias voltage is then set toproduce the ion bombardment energy desired.

FIG. 2B shows a top view of the FIG. 2A source with the top cover 72 andtarget 83 removed. This view shows one embodiment of magnet array 80 toproduce a uniform coating on the wafer surface. This ‘comma’ magnetpattern is designed so that by rotating stage 75 about its central axis,the deposition on the wafer is uniform.

FIG. 2C shows an exploded isometric view of the IPVD source. In FIG. 2C,the wafer substrate 76 is centered on stage 75. Magnet array 80 rotatesunder the stage 75 resulting in confined plasma 77 rotating over wafer76. While the ‘comma’ type magnet array design of FIG. 2B is useful toproduce uniform sputtered coatings on wafer 76, many other magneticconfigurations can be implemented to achieve uniform deposition whilemaintaining the basic inventive method of mirror confinement Othermagnet array embodiments include a linear magnet array scanned under arectangular shaped stage. A curved magnet array similar to the ‘comma’shaped field shown in FIG. 2B can be translated as well as rotated toimprove uniformity at the center point on the wafer.

In the FIGS. 2A, 2B and 2C source, the magnet material is a rare earthtype. The field 78 produced between the wafer and electrode 72 isgreater than 100 gauss—in other words, the plasma electrons are“magnetized” in the gap. Using today's materials, it is relatively easyto increase the magnetic field strength to also magnetize the plasmaions. This requires a magnetic field strength nearing or greater than1000 G. The plasma of the method of the preferred embodiment adapts wellto ion magnetization because there are no cathode surfaces to interrupta larger gyro radius as with a planar magnetron type confinement.

Where prior art sources have used magnets under the wafer to directplasma down onto the wafer from another plasma source, Applicant'smethod produces a dense plasma in and of itself, the dense plasmaforming directly over the wafer surface. The benefits of focusing theelectron and ion flow down on the wafer are fully realized usingApplicant's method. As shown by switch 83 and bias power supply 82, theinventive method allows for platen 75 and wafer 76 being either leftfloating, grounded or positively or negatively biased by supply 82.

The present invention has advantages for sputtering and IPVD processes.As described earlier, the impedance of the magnetic mirror source ishigher than a magnetron cathode sputter source. One aspect of higherimpedance is a higher operating voltage. For sputtering this can be anadvantage because sputter yield rates rise significantly as voltageincreases. Therefore, the sputter rate with the mirror source is higherin this regard.

The electron confinement of the present invention produces a denseplasma cloud between the sputter target and substrate. By operating themirror source at higher pressures, for instance, 30 mTorr, a largenumber of neutral metal flux atoms ejected at the target are ionizedbefore reaching the substrate. Significant ionization is apparent when,while sputtering copper in argon, the plasma in the magneticallyconfined region is bright green in color.

Magnetic materials can be sputtered as easily as non-magnetic materials.This is a major benefit of the present invention as applied tosputtering processes.

The target utilization is improved over magnetron sputtering. As is wellknown with magnetron sputtering, a deep racetrack groove forms as thetarget is eroded. This self-perpetuating effect results in poor usage ofexpensive sputter materials. The mirror source on the other hand tendsto erode the target relatively evenly over the entire sputtered region.Not only is target utilization improved but the net sputter rate on thesubstrate does not vary over time.

FIG. 3A is a section view of a sputter source comprising an embodimentfor use with large planar substrates. In this case substrate 1 may be arigid planar substrate or a web tensioned to be planar between twocontinuously moving rolls. Substrate 1 is in proximity to shield 8 butis far enough away to allow the substrate 1 to be conveyed withoutscrapping shield 8. A magnetic field 12 is set up between the substrateand sputter target 83 by permanent magnets 5, 6, and 7, magnetic shunts2 and 4 and cathode shunt 3. The field 12 is shaped into a “shower head”mirror field with the substrate 1 located at the compressed end.

An electric field 15 is created by power supply 16 between cathodetarget 83 and the chamber ground. Shields 9, 10 and 11 are connected toground. Magnet shunt 4 and shield 8 electrically float Power supply 16can be DC even in the case of a dielectric substrate because there is nocurrent flow to shield 8. Alternatively, in the case where a dielectriccoating is being sputtered, a pulsed DC or AC power supply 16 can beused.

The plasma 13 is confined by the magnetic field 12, cathode target 83,and the magnetic mirror at the substrate 1. The electrons are trapped inthe dimension out of or into the paper by electric field lines 15 thatcontinuously circumvent the magnetic field 12 all around magnetic field12. The result is that Hall current 14 created by the electronconfinement is trapped into a continuous loop within the magnetic field12. At low powers, this containment ring is readily apparent to the eye.At higher powers, the plasma expands to fill the region 13 between thesubstrate and target 83.

Note that the anode is the chamber wall and grounded shields. Thisprovides sufficient electric field penetration into the gap betweencathode target 83 and substrate 1 for the plasma confinement effects.The gap between cathode 83 and the substrate 1 must be sufficient tostrike a plasma. The gap size is also based upon the necessity to createa strong mirror magnetic field between surfaces 83 and 1, the need for amagnetic field sufficient to magnetize at least electrons, and to enableobservation of the plasma from a view port. A typical gap is about 2inches.

A source like that in FIG. 3A was built with a 4″ long ceramic magnet 7(out of the paper) and an 8″ long cathode shunt 3 with a similar sizedsputter target 83 bonded to shunt 3. With the chamber pressure at 20mTorr and a voltage of approximately 800V impressed between cathode 83and ground, a bright plasma is maintained over substrate 1 as shown. Tostart the discharge, the pressure may have to be spiked depending uponthe ignition voltage of the power supply. While specific values aregiven here, different pressures, voltages, frequencies and power levelscan be used depending upon the process gas, substrate thickness andmaterial, magnetic fields and other variables. The values given areintended to provide the engineer with starting values to demonstrate thepreferred embodiment. As with traditional magnetron confinement, theoperating values can vary widely while still receiving the benefits ofthe preferred embodiment.

FIG. 3B is an isometric view of an extended FIG. 3A plasma source. Inthis view, one can see that the plasma Hall current is contained withinthe dipole magnetic field bounded by substrate 1 and sputter target 83.The magnetic field is generated by magnets 5, 6, and 7 and is assistedby high permeability shunts 2, 3 and 4. Note that with this dipolearrangement, magnet pole 7 simply ends near the edge of the substrate.The magnetic field 12 in the gap extends from permanent magnet 7 tocathode 83 to create one extended showerhead mirror magnetic field.Within this field, Hall currents are confined into an endless loopcreating intense plasma 13. Substrate 1 is conveyed over magnet poles 6and 7 and shield 8. The gap between shields 8 and 9 is small to minimizespurious plasma generation while allowing the substrate to pass throughunobstructed. Shield 10 and 11 may receive enough heat to require watercooling. This is largely dependent upon the type of process, powerlevels, materials and factors relating to the configuration of theplasma contacting surfaces, fields, etc.

For most industrial processes with long process runs and high powers,all electrodes must be water cooled using known techniques. Note thatthe FIG. 3B source is depicted longer than the 4 inch long ceramicmagnet described. The source is shown longer to illustrate the abilityof the present invention to be extended to large area substrates. Toscale the FIG. 3B view, the gap between the substrate 1 and shield 11(the sputter target 83 can not be seen in this view) is about 2 inches.

FIG. 4 shows a section view of another planar source embodiment. In thissource two magnetic mirror regions 14 and 34 are created within onemagnetic field circuit. Two sputter cathodes 35 and 36 are connectedacross a mid-frequency (50-450 kHz) power supply 16 similar to a dualmagnetron configuration known in the art. Like the dual magnetronconfiguration, reactive, insulating coatings can be sputtered becauseeach source alternates as both an anode and cathode. In the cathodemode, ion impingement tends to ablate and clean the electrode so thatanode conductivity is maintained over extended production runs.

The magnetic circuit consists of high permeability shunt 37, magnet 27,mirror plasma gap 34, shunt 23, shunt 38, shunt 3, mirror plasma gap 14and magnet 7. Substrate 1 is conveyed over water cooled non-magneticblock 31 without touching block 31 by conveyor rolls not shown. Block 31is water cooled by drilled hole 33 and water piping not shown. Sputtertargets 35 and 36 are bonded to water cooled backing plates 30. Watercooling of sputter targets is well known and details are not shown.Backing plates 30 are fastened to high permeability shunts 3 and 23.

While many configurations are possible to produce the magnetic mirroreffect of the present invention, the use of a high permeability shuntplates 3 and 23 at the expanded end of the magnetic mirror works well tocollect the magnetic flux lines 12 and 32 coming out of magnets 7 and 27respectively and produce the champagne glass looking magnetic mirrorfields 12 and 32 shown. When power supply 16 is turned on and processgas maintains the process chamber at ˜5-100 mTorr, plasmas 14 and 34light. Power supply 16 may be set to a wide range of frequencies.Readily available AC sputter power supplies have frequency ranges from20 kHz to 460 kHz. This frequency range works well for sputtering aswell as PECVD or reactive ion etching processes. RF frequencies, forinstance 13.56 MHz, can also be used.

The source of FIG. 4 can be extended to any width required in the sameway a magnetron sputter cathode can be extended. In this case, the dualgap magnet arrangement is lengthened under the substrate and theparallel sputter cathode arrangement over the substrate is equallyextended. As with a magnetron cathode, the confined Hall current movingaround the “racetrack” provides an inherent uniformity across the lengthof the source. By moving the substrate orthogonal to the extended plasmaregions 14 and 34, a uniform sputter coating of the substrate 1 isobtained.

FIG. 5 shows a section view of a web coating apparatus embodiment. Inthis embodiment, web 100 is moved continuously over rolling support 102.Roll 102 contains permanent magnet and magnet shunt assembly 111. Roll101 has an inner steel roller 121 of sufficient thickness to carrymagnetic field 108 and is covered by material to be sputtered 111. Roll101 is rotated to increase the time between target changes and to assistwith target cooling. Cooling water is circulated through both thecathode inner steel roller, 121 and web supporting roller 102.

Rotating sputter targets are well known in the art. Magnetic field 108is created in the gap between rolls 101 and 102 by magnetic assembly111, steel roll 101, magnet shunt pieces 106 and 107, permanent magnets104 and 105 and magnetic shunt 103. Due to the different polestructures, magnetic field 108 is not a symmetrical mirror field buttakes on the appearance of a showerhead. Roll 101 is connected to powersupply 110 as the cathode electrode and roll 102 can either be leftelectrically floating, connected as an anode in the electrical circuit120, or connected in parallel with roll 101 as the cathode.

Different outcomes result and offer different advantages depending uponprocess requirements. When roll 102 is left floating, an electron trapis maintained by the magnetic mirror effect as electrons approach thecompressed magnetic field 108 at the roll 102 surface and by thephysical presence of web 100 on roll 102. The magnetic field 108 issurrounded by electric field 118 so that Hall currents are containedwithin magnetic field 108, and an intense plasma 109 is created. In thisembodiment, magnetic pole pieces 106 and 107 are electrically floating,permanent magnets are ceramic type and are not electrically conductive,and magnetic shunt 103 is connected to the chamber ground.

Roll 101 must be connected as a cathode. Roll 102, with the strongermagnetic field, can be connected as the anode, cathode or floating.Power supply 110 can be DC, pulsed DC, mid frequency AC or RF. In thecase of metal conducting sputtering applications, a DC power supplyworks well. The source of FIG. 5 shows the present invention implementedwith a rotating sputter target. Many combinations and variations arepossible within the scope of the present invention. For example, dualrotating targets can be implemented with the source configuration shownin FIG. 4.

FIG. 6 depicts another sputter source embodiment. In this source, twomagnets are disposed across a gap. Sputter cathode electrode 45 islocated approximately in the center of the gap. Electrode 45 isconstructed of copper, stainless steel, titanium or other non-magneticmaterial to be sputtered. As can be seen, a mirror magnetic field isgenerated with the compressed field passing through the substrate 41 andthe less compressed field passing through the cathode electrode 45. Whenvoltage from a power supply 42 is impressed across the cathode electrode45 and a ring anode 43 such that electric fields penetrate into themagnetic field sufficiently, the electron Hall current is containedwithin the magnetic field. With sufficient voltage and process gaspressure, a plasma 44 is formed between the cathode and substrate. FIG.6 illustrates that magnetic arrangements other than a high permeabilitycathode can be implemented. In this source, target 45 is bonded to watercooled backing plate 48.

All the embodiments of the invention include a high permeability memberor permanent magnet at the uncompressed, cathode electrode end of themagnetic field. This configuration pulls the magnetic field from themagnet under the substrate, through the gap and into the cathodeelectrode. An alternative is to position only a non-magnetic electrodeover the substrate. For instance, in FIG. 6 magnet 40 could be removed.The magnetic field would primarily loop around from the north pole tosouth pole of magnet 47. A small portion of the field would pass fromthe north pole of magnet 47 and, before arriving at the south pole, passthrough cathode surface 45. If this field is strong enough to magnetizeelectrons, a plasma per the inventive method will form. Again, becauseof the relative simplicity of using a magnetic material in the cathode45 ‘assembly’ and the benefit of increasing the field lines into thecathode, a magnetic material is preferred.

In certain embodiments, cathode surface 45 is moved closer to magnet 40.In this configuration, the electrons moving toward the substrate aremoving from a region of weak magnetic field to a stronger field (with aratio in excess of 1:2).

The combined Lorentz and magnetic mirror electron confinementarrangement trap the Hall current in a racetrack orbit directly over thesubstrate. Of similar magnitude to Penning's work in the 1930's, thisconfinement regime opens doors to a wide range of processes andtechnologies producing results not resembling known prior art Manyapplications for sputtering, PECVD, plasma etching and plasma treatmentwill be substantially improved or made possible. Also, the new sourcecan be combined with other plasma sources to improve upon or create newplasma sources. While many benefits to this new technology will befound, some of the benefits include:

-   -   For sputtering applications, the confinement of electrons in the        gap between the sputter target and substrate increases the        degree of ionization of the sputtered flux. This can be useful        for many applications.    -   Magnetic materials can be sputtered as readily as non-magnetic        materials. In sputter magnetrons, magnetic materials are        difficult to sputter because the target must be saturated before        the electron confining racetrack magnetic field permeates        through the target. In the present invention, the orthogonal        positioning of the magnetic field obviates this problem.    -   The magnetic and electric field confinement geometry produces a        symmetrical, endless racetrack confinement zone similar to a        planar magnetron sputtering device or a grid-less ion source. As        is known in these technologies, the length of the confinement        zone can be extended to accommodate wide substrates while        maintaining a uniform plasma. This is a major improvement over        unconfined RF or microwave discharges for large substrates at        significantly less cost.    -   As a true magnetically enhanced plasma source, the efficient        plasma confinement allows operation at low pressures and        voltages. Many process advantages are gained by this. Plasma        does not light in other parts of the chamber or on electrode        surfaces outside of the containment zone. The plasma is        characteristically stable and uniform. Lower plasma voltage        requirements make the power supplies safer and less costly.    -   The technology is adaptable to different process substrate        energy requirements. As shown in the figures, the substrate can        be floating, biased negatively, or biased positively to produce        different results.

Finally, it should be noted that any of the alternatives discussed abovecan be used alone or in combination with one another. Some of thesealternatives include:

-   -   The surface of the cathode electrode can be planar, curved, a        rotating roll, beveled or a variety of other shapes.    -   The substrate can be biased positively, tied to ground, left        floating, or biased negatively.    -   AC or RF voltage can be used to bias the substrate. If the        substrate is electrically conductive, DC can be used to bias the        substrate.    -   DC, AC, or RF can be used to power the cathode electrode        depending upon the application.    -   The magnetic field can be moved relative to the substrate        instead of the substrate moving relative to the magnetic field.    -   The magnetic field can be made with high permeability materials        and magnets both above and below the substrate or just below the        substrate.

While the preferred embodiments of the present invention have beenillustrate in detail, it should be apparent that modifications andadaptations to those embodiments may occur to one skilled in the artwithout departing from the scope of the present invention as set forthin the following claims.

1. A plasma source apparatus comprising: a substrate having a firstsurface and an opposing surface; a second surface, said second surfacebeing spaced apart from said first surface by a predetermined gap,connected to a power supply as a cathode; a third surface connected tothe power supply as an anode; a magnetic field source comprising apermanent magnetic oriented with a north pole proximal to said substraterelative to a south pole and providing a magnetic field axial with saidmagnetic field source, said magnetic field passing into both said firstand second surfaces and through said gap, said magnetic field having aportion passing through said substrate that is at least two timesstronger at said first surface than at said second surface, saidmagnetic field portion having a strength strong enough to magnetizeelectrons; and an electric field extending to said second surface andsaid electric field penetrating into an electron confining region ofsaid magnetic field to confine the electrons electrostatically and withmirror magnetic confinement.
 2. A plasma source apparatus in accordancewith claim 1, wherein: said electric field extends to said substrate. 3.A plasma source apparatus in accordance with claim 1, comprising: achamber, said chamber containing said first and second surfaces; andsaid electric field extends from said chamber to said substrate.
 4. Aplasma source apparatus in accordance with claim 1, comprising: saidsubstrate moving continuously relative to said magnetic field.
 5. Aplasma source apparatus in accordance with claim 1, wherein: saidsubstrate has said first surface parallel to said opposing surface.
 6. Aplasma source apparatus in accordance with claim 1, wherein: saidsubstrate is biased positively.
 7. A plasma source apparatus inaccordance with claim 1, wherein: said substrate is tied to ground.
 8. Aplasma source apparatus in accordance with claim 1, wherein: saidsubstrate is left floating.
 9. A plasma source apparatus in accordancewith claim 1, wherein: said substrate is biased negatively.
 10. A plasmasource apparatus in accordance with claim 1, wherein: said substrate isbiased with an AC voltage.
 11. A plasma source apparatus in accordancewith claim 1, wherein: said first and second surfaces are parallel. 12.A plasma source apparatus in accordance with claim 1, wherein: saidfirst and second surfaces are non-parallel.
 13. A plasma sourceapparatus in accordance with claim 1, wherein: said substrate comprisesa flexible web supported by a conveyor roll.
 14. A plasma sourceapparatus in accordance with claim 1, comprising: a mirror field shapedinto a racetrack and having a return field passing through the center ofthe racetrack.
 15. A plasma source apparatus comprising: a substratehaving a first surface and an opposing surface; a second surface, saidsecond surface being spaced apart from said first surface by apredetermined gap, connected to a power supply as a cathode; a thirdsurface connected to the power supply as an anode; a permanent magnetoriented with a north pole proximal to said substrate relative to asouth pole and under said substrate providing a magnetic field axialwith said permanent magnet under said substrate, said magnetic fieldpassing into both said first and second surfaces and through said gap,said magnetic field having a portion passing through said substrate thatis at least two times stronger at said first surface than at said secondsurface, said magnetic field portion having a strength strong enough tomagnetize electrons; and an electric field extending to said secondsurface and said electric field penetrating into an electron confiningregion of said magnetic field to confine the electrons electrostaticallyand with mirror magnetic confinement.
 16. A plasma source apparatus inaccordance with claim 15, wherein: said electric field extends to saidsubstrate.
 17. A plasma source apparatus in accordance with claim 15,comprising: a chamber, said chamber containing said first and secondsurfaces; and said electric field extends from said chamber to saidsubstrate.
 18. A plasma source apparatus in accordance with claim 15,comprising: relative movement between said substrate moving continuouslyrelative to said magnetic field.
 19. A plasma source apparatus inaccordance with claim 15, wherein: said substrate is biased negatively.20. A plasma source apparatus in accordance with claim 15, wherein: saidsubstrate is biased with an AC voltage.
 21. A plasma source apparatus inaccordance with claim 15, wherein: said first and second surfaces areparallel.
 22. A plasma source apparatus in accordance with claim 15,wherein: said substrate comprises a flexible web supported by a conveyorroll.
 23. A plasma source apparatus in accordance with claim 15,comprising: a mirror field shaped into a racetrack and having a returnfield passing through the center of the racetrack.